This application claims the priority of Korean Patent Application No. 2002-36070, filed Jun. 26, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a circuit and method for controlling the vertical and horizontal sizes of a screen of a cathode ray tube (CRT) monitor, and more particularly, to a circuit for controlling the vertical and horizontal sizes of the screen of a CRT monitor in order to compensate for changes in the vertical and horizontal screen sizes of a CRT monitor due to variations in high voltage in the CRT monitor.
2. Description of the Related Art
CRT monitors are commonly receive a power supply voltage from a switched mode power supply (SMPS), which is a form of a power supply circuit.
Here, since the anode of the CRT monitor requires a high voltage, the highest voltage among power supply voltages output from the SMPS is usually stepped up by a flyback transformer (FBT) and the stepped-up voltage is applied to the anode.
However, when high voltage is generated using the FBT, if the level of the high voltage is decreased or fluctuates even slightly, the horizontal and vertical sizes of the screen of the monitor can become distorted. That is, a variation in the level of the high voltage directly affects the horizontal and vertical sizes of the screen of a monitor.
FIG. 1 is a block diagram of the internal structure of a typical CRT monitor. Referring to FIG. 1, a CRT monitor 100 includes a microcomputer (MICOM) 110, a sync processor 120, horizontal and vertical drivers 125 and 130, a video amplifier (video amp) 165, a video driver 170, an electron gun 175, vertical and horizontal deflection coils 185 and 190, a CRT 180, a deflection regulator 135, a B+ voltage generator 140, a switching power circuit 145, a high voltage regulator 150, a FBT 160, and an anode 195.
The sync processor 120 receives a vertical synchronization signal VIN and a horizontal synchronization signal HIN and generates a vertical output signal VOUT, a horizontal output signal HOUT, and an east-west correction signal EWOUT under the control of the MICOM 110.
The horizontal driver 125 controls the horizontal deflection coil 190 in response to the horizontal output signal HOUT in order to control the horizontal size of the screen of a monitor 180. The vertical driver 130 controls the vertical deflection coil 185 in response to the vertical output signal VOUT in order to control the vertical size of the screen of the monitor 180.
A color signal RGB is applied to the electron gun 175 via the video amp 165 and the video driver 170.
The deflection regulator 135 is controlled by the SMPS 145 and controls the B+ voltage generator 140 in response to the east-west correction signal EWOUT. The FBT 160 is controlled by the high voltage regulator 150 and applies high voltage to the anode 195.
The CRT monitor 100 generates a high voltage to form a magnetic tunnel and projects electrons output from the electron gun 175 through the formed magnetic tunnel to the screen. If a change in the level of the high voltage occurs due to an overload or if a characteristic change due to a high temperature occurs when the high voltage is generated, the screen becomes distorted and the quality of an image is therefore deteriorated.
The sync processor 120 performs various operations to compensate for the anticipated distortion of the screen and the degradation of the image quality. In particular, when the screen is distorted due to a decrease in the DC voltage of the generated high voltage, the sync processor 120 performs extreme high transformer (EHT) compensation to compensate for such distortion.
Generally, the horizontal size of the screen is controlled based on the DC voltage of an east-west correction signal, and the vertical size of the screen is controlled based on the gain of the vertical output signal VOUT output from the sync processor 120. EHT compensation controls the DC voltage of the east-west correction signal EWOUT and the gain of the vertical output signal VOUT.
To be more specific, the output of the high voltage regulator 150 is fed back as a DC voltage to the sync processor 120. The sync processor 120 controls the level of the DC voltage of the east-west correction signal EWOUT using the fed-back DC voltage in order to compensate for the horizontal size of the monitor screen. Also, the sync processor 120 controls the vertical output signal VOUT in order to compensate for the vertical size of the monitor screen.
The horizontal size of the monitor screen is controlled using the DC voltage component of the east-west correction signal EWOUT, which is generally used to correct the geometry of the right and left sides of the screen. That is, the alternating current (AC) component of the east-west correction signal EWOUT is used for geometry correction.
The vertical size of the monitor screen is controlled based on the gain of the vertical output signal VOUT, and the DC voltage of the vertical output signal VOUT controls screen shifting.
During EHT compensation, the horizontal size of the screen is controlled according to a horizontal screen size correction signal HEHT, and the vertical size of the screen is controlled according to a vertical screen size correction signal VEHT.
However, since a typical CRT monitor pre-determines the degree of EHT compensation to be controlled, uniform compensation is applied for a variety of CRT monitors.
FIG. 2 is a graph showing the characteristics of conventional HEHT compensation. The horizontal size correction signal HEHT in the high voltage regulator 150 does not affect the CRT monitor system when the voltage value of the horizontal size correction signal HEHT is greater than or equal to the level of a horizontal reference voltage REFEHT that is set to be a threshold voltage.
As the voltage value of the horizontal size correction signal HEHT decreases below that of the horizontal reference voltage REFEHT, the amount of current of a horizontal current signal IO needed for compensating for the horizontal size of a monitor screen increases. When the voltage value of the horizontal size correction signal HEHT is 0V, the amount of current of the horizontal current signal IO is at a maximum.
In other words, the current value of the horizontal current signal IO increases in proportion to the difference between the voltage value of the horizontal size correction signal HEHT and the voltage value of the horizontal reference voltage REFEHT. The compensation characteristics of FIG. 2 also apply to the characteristics of a vertical size correction signal VEHT.
However, as can be seen from the graph of FIG. 2, since the degree of EHT compensation (i.e., the slope of the straight line of FIG. 2) to be pre-set in a CRT monitor is fixed, uniform compensation is applied to a variety of CRT monitors. For this reason, CRT monitor manufactures are not able to apply compensation that depends on unique and specific requirements of each particular CRT unit.
The present invention provides a circuit for controlling the vertical and horizontal screen sizes of a cathode ray tube (CRT) monitor by variably adjusting the degree of extreme high transformer (EHT) compensation.
The present invention also provides a method of controlling the vertical and horizontal screen sizes of a CRT monitor by variably adjusting the degree of EHT compensation.
According to an aspect of the present invention, there is provided a circuit for controlling the horizontal and vertical sizes of a screen of a cathode ray tube (CRT) monitor, the circuit including a horizontal screen size compensation circuit, an east-west correction signal controller, a vertical screen size compensation circuit, and a vertical screen size correction signal controller.
The horizontal screen size compensation circuit compares the voltage value of a horizontal screen size correction signal with the voltage value of a horizontal reference voltage to obtain first and second horizontal current signals, and, in response to a horizontal control signal, generates a horizontal correction current signal by subtracting a horizontal variable current signal from the first horizontal current signal, and outputs the horizontal correction current signal.
The east-west correction signal controller generates an east-west direct current (DC) correction signal by combining the horizontal correction current signal with an east-west DC gain signal.
The vertical screen size compensation circuit compares the voltage value of a vertical screen size correction signal with the voltage value of a vertical reference voltage to obtain a vertical current signal, which in one embodiment, may comprise first and second vertical current signals, generates a vertical correction current signal as a function of the vertical current signal(s) and a vertical control signal, and outputs the vertical correction current signal.
The vertical screen size correction signal controller compares a sawtooth voltage signal with a sawtooth reference voltage, amplifies the difference, converts the amplified signal into a sawtooth current signal, and generates a vertical screen size control signal by subtracting the vertical correction current signal from the sawtooth current signal.
The horizontal screen size compensation circuit includes first and second comparators, a first digital-to-analog converter, a horizontal variable current signal generator, and a horizontal correction current signal generator.
The first comparator receives the horizontal reference voltage via its positive terminal and the horizontal screen size correction signal via its negative terminal and outputting the first horizontal current signal. The second comparator receives the horizontal reference voltage via its positive terminal and the horizontal screen size correction signal via its negative terminal and outputs the second horizontal current signal.
The first digital-to-analog converter receives the horizontal control signal and generates a horizontal control current signal used to generate the horizontal variable current signal. The horizontal variable current signal generator generates the horizontal variable current signal by dividing the current value of the second horizontal current signal by the current value of the horizontal control current signal.
The horizontal correction current signal generator generates the horizontal correction current signal by subtracting the current value of the horizontal variable current signal from the current value of the first horizontal current signal.
The current value of the first horizontal current signal is greater than or equal to the current value of the horizontal variable current signal. As the value of the east-west DC correction signal increases, the horizontal screen size of the CRT monitor decreases.
The horizontal correction current signal varies between the current value of the first horizontal current signal and the current value obtained by subtracting the current value of the horizontal variable current signal from the current value of the first horizontal current signal.
The horizontal screen size correction signal is a voltage signal that is generated by a high voltage regulator and fed back. The horizontal control signal is an I2C signal generated by a microcomputer.
The vertical screen size compensation circuit includes third and fourth comparators, a second digital-to-analog converter, a vertical variable current signal generator, and a first vertical correction current signal generator.
The third comparator receives the vertical reference voltage via its positive terminal and the vertical screen size correction signal via its negative terminal and outputs the first vertical current signal. The fourth comparator receives the vertical reference voltage via its positive terminal and the vertical screen size correction signal via its negative terminal and outputs the second vertical current signal.
The second digital-to-analog converter receives the vertical control signal and generates a vertical control current signal used to generate the vertical variable current signal. The vertical variable current signal generator generates the vertical variable current signal by dividing the current value of the second vertical current signal by the current value of the vertical control current signal.
The first vertical correction current signal generator generates the first vertical correction current signal by subtracting the current value of the vertical variable current signal from the current value of the first vertical current signal.
The current value of the first vertical current signal is greater than or equal to the current value of the vertical variable current signal.
The vertical screen size compensation circuit further includes a second vertical correction current signal generator and a mode selector. The second vertical correction current signal generator generates the second vertical correction current signal by adding the current value of the vertical variable current signal to the current value of the first vertical current signal. The mode selector outputs the second vertical correction current signal as the vertical correction current signal in response to an external selection signal.
As the value of the vertical screen size control signal increases, the vertical screen size of the CRT monitor increases. The vertical correction current signal varies between the current value obtained by subtracting the current value of the vertical variable current signal from the current value of the first vertical current signal and the current value obtained by adding the current value of the vertical variable current signal to the current value of the first vertical current signal, and the current value of the first vertical current signal is the middle value of the variation range.
The vertical screen size correction signal is a voltage signal that is generated by a high voltage regulator and fed back. The vertical control signal is an I2C signal (inter-integrated circuit) generated by the microcomputer.
According to another aspect of the present invention, there is provided a method of controlling the horizontal screen size of a CRT monitor, according to a first embodiment of the present invention. In the method, first, the current value of a horizontal screen size correction signal, for example, such a signal as fed back from a high voltage regulator, is compared with the current value of a horizontal reference voltage to obtain first and second horizontal current signals. Next, a digital horizontal control signal is converted into an analog horizontal control current signal. Thereafter, a horizontal variable current signal is generated by dividing the current value of the second horizontal current signal by the current value of the horizontal control current signal. Then, a horizontal correction current signal is generated by subtracting the current value of the horizontal variable current signal from the current value of the first horizontal current signal. Then, an east-west DC correction signal is generated by combining the horizontal correction current signal with an east-west DC gain signal.
The current value of the first horizontal current signal is greater than or equal to the current value of the horizontal variable current signal. As the value of the east-west DC correction signal increases, the horizontal screen size of the CRT monitor decreases.
The horizontal correction current signal varies between the current value of the first horizontal current signal and the current value obtained by subtracting the current value of the horizontal variable current signal from the current value of the first horizontal current signal.
The horizontal control signal is an I2C signal generated by a microcomputer.
According to another aspect of the present invention, there is also provided a method of controlling the vertical screen size of a CRT monitor, according to a second embodiment of the present invention. In the method, first, the current value of a vertical screen size correction signal, for example, such a signal as fed back from a high voltage regulator, is compared with the current value of a vertical reference voltage to obtain first and second vertical current signals. Next, a digital vertical control signal is converted into an analog vertical control current signal. Thereafter, a vertical variable current signal is generated by dividing the current value of the second vertical current signal by the current value of the vertical control current signal. Then, either a value obtained by subtracting the current value of the vertical variable current signal from the current value of the first vertical current signal or a value obtained by adding the current value of the vertical variable current signal to the current value of the first vertical current signal is output as a vertical correction current signal. Then, a sawtooth voltage signal is compared with a sawtooth reference voltage to determine the difference therebetween, the difference is amplified, and the amplified signal is output as a sawtooth current signal. A vertical screen size control signal is generated by subtracting the vertical correction current signal from the sawtooth current signal.
The current value of the first vertical current signal is greater than or equal to the current value of the vertical variable current signal. As the value of the vertical screen size control signal increases, the vertical screen size of the CRT monitor increases.
The vertical correction current signal varies between the current value obtained by subtracting the current value of the vertical variable current signal from the current value of the first vertical current signal and the current value obtained by adding the current value of the vertical variable current signal to the current value of the first vertical current signal, and the current value of the first vertical current signal is the middle value of the variation range.
The vertical control signal is, for example, an I2C signal generated by a microcomputer.